Hybrid ARQ (HARO) has been shown to provide advantages in communication system throughput, and has been shown to make the system robust to modulation and coding scheme (MCS) selection errors. Full Chase combining is the simplest form of HARQ. In the full Chase combining scheme, retransmissions of information are simply repetitions of the initial transmission. A Chase HARQ decoder is easier to implement than a full incremental redundancy (IR) HARQ decoder because the joint transmission decoder for Chase combining consists of a single soft storage buffer and soft combiner followed by the decoder that was used for the first transmission. For IR, soft storage must be provided for each transmission (i.e., no combining is performed), and the joint decoder must process all received data.
Full Chase HARQ has been implemented in a transmitter/receiver chain of a communications device such as that shown in FIG. 1. The channel encoder and decoder blocks may include functions such as cyclic redundancy check (CRC) coding and rate-matching as well as forward error correction (FEC) coding with a turbo, convolutional, Bose-Chaudhuri-Hocquenghem (BCH), or other code (including adding tail bits, if any). The block interleaver and deinterleaver reorder the bits/values received to help the channel encoder and decoder provide a diversity benefit. The modulator and demodulator blocks may include QPSK, 8PSK, MQAM, or other modulations, as well as Walsh code demultiplexing and spreading. The full Chase combining function can occur before or after the block de-interleaver as known in the art.
A potential drawback of full Chase HARQ is that every retransmission of information must be the same size as the original transmission. With certain combinations of traffic, such as voice and supplemental channel data, the available channel resources, such as code space, time slots, frequency channels, or streams, may change causing current HARQ transmissions to abort because of insufficient code space for further retransmissions. Similarly, changes in the code space may provide additional code resources that a current user cannot take advantage of because in full Chase HARQ, retransmissions are the same size as the initial transmission.
Thus, there is a need for an apparatus and method for transmitting and receiving data, wherein retransmissions of information can be a different size from the initial transmission.